1. Field of Invention
The disclosed invention is an aqueous polymeric vehicular emulsion composition containing suspended electrically conductive material. The present invention is particularly relevant to the field of electronics and other electrical applications, such as printed circuit boards, EMI & RFI shielding and electrochemical fuel cell applications.
2. Description of Prior Art
The electronics industry and its peripheries annually spend substantial resources on manufacturing processes and materials. Many of these processes and materials are expensive and environmentally hazardous. For example, two fields of the electronics industry, circuit board etching and Electro-Magnetic Interference (EMI) shielding, regularly use expensive and toxic chemicals in product fabrication. A circuit board is produced using expensive caustic acids to etch away the photo-reactive metallic layer from the circuit board substrate. The by-products of this process are typically expensive to recycle or else non-recyclable and require costly disposal programs.
Another form of circuitry is the hybrid ceramic circuit utilized in specialized niche markets in electronics industries. Hybrid ceramic circuits are expensive, requiring extremely high constant temperatures to manufacture. They typically are utilized as miniature circuit boards employed as components on larger circuit boards wherein space is a critic factor. However, the high cost of manufacturing hybrid ceramic circuits is prohibitive to widespread commercial use. EMI shielding is incorporated extensively in electronics. It is an integral part of computers, medical equipment and any other EMI sensitive electronics. Electromagnetic interference from the environment or from internal sources, such as high-speed circuits, can disrupt numerous electronics. Often, entire systems must be shielded in order to minimize EMI. Prior art methods of shielding electronics from EMI leave significant room for improvement. For example, the high-speed circuits are often simply isolated and removed as far as possible from the other, more sensitive electronics. Another method is to incorporate metal boxes onto the circuit boards themselves to directly shield the sensitive electronics. However, propinquity and the potential for material compatibility conflicts may be inappropriate or unacceptable for numerous applications. Yet, another method of producing EMI shielding utilizes Chemical Vapor Deposition (CVD) of copper onto the substrate to be shielded. This method of EMI shielding is expensive and creates environmentally hazardous by-products. A more effective method for manufacturing EMI shielded products utilizes electrically conductive polymers to coat the substrate that is to be shielded. However, the majority of these polymers use Volatile Organic Compounds (VOCs) as solvents to emulsify the polymer and electrically conductive material.
These harsh acids and VOC solvents are initially expensive to purchase. Their recycle or disposal is also expensive because they are environmentally hazardous. Likewise, they are also health hazards due to their generally toxic and/or flammable compositions. U.S. Pat. Nos. 5,492,653 and 5,658,499 are examples of prior art that posit the inclusion of water-miscible VOCs in water-based electrically conductive compositions to be employed in the electronics industry. However, VOCs commonly become trapped within solvent-based polymer compositions, including electrically conductive polymer compositions. The trapped solvents attack any metallic electrically conductive material and diminish or arrest its electrically conductive functionality, thereby compromising the efficacy of the electrically conductive composition as such. Moreover, the use of any VOCs is prohibited in industries, such as the Proton Exchange Membrane (PEM) fuel cell industry, wherein the components of the apparatus are extremely susceptible to corrosion caused by organic solvents.
In summation, it is manifest from prior art that an inexpensive, non-toxic alternative to these chemicals and processes would greatly improve several facets of the electronics industry. A less expensive electrically conductive multi-functional material would reduce production expenditures; a non-toxic alternative would mean less drastic and less expensive recycle and disposal programs. Such an alternative that is concurrently inexpensive and non-toxic would redouble the benefit to the electronics industry. Yet, heretofore no feasible alternative existed in the electronics industry.
The present invention embodies one such solution to the aforementioned problems of expensive and hazardous materials utilized in the electronics industry. The invention is relevant to the utility of water-based polymers—exclusive of water-miscible VOCs—as a vehicle for electrically conductive materials. This novel electrically conductive polymer can then be applied to an extensive number of substrates in order to impart electrical conductivity for numerous applications. This novel invention will reduce material expenditures and alleviate costly recycle and disposal programs.
There are industries, other than the electronics industry, that also would benefit from an electrically conductive water-based polymer technology. One such industry is the electrochemical fuel cell industry, especially the PEM fuel cell industry. PEM fuel cells constructions would benefit from electrically conductive sealants in order to seal the components in a fuel cell stack. Due to the novel and unobvious composition of the present invention, it is adept as an electrically conductive sealant within PEM fuel cells. Likewise, there are several other industries or markets that could utilize the present invention such as sensors, structural integrity sensor matrices, and electrical contacts.